The goal of ginning is to produce a high quality product for the mills at a profit for the gin. The quality of the lint produced by a gin is dependent on the initial seed cotton quality and on the type and degree of cleaning and drying performed at the gin plant. Both the efficiency of the cleaning machines and damage done to the cotton fibers during cleaning and ginning are strongly influenced by the fiber moisture content during processing (Mangialardi and Griffin; 1977; Restoring Moisture to Cotton at Midsouth Gins; USDA Technical Bulletin No. 1553). Griffin (1977; Cotton Ginners Handbook. USDA Handbook No. 503, pp. 13-17) reported that the moisture content of cotton lint should be in the range of 6.5 to 8 percent to maintain optimum fiber quality. In order to maintain a lint moisture in this range the drying equipment needs to be adjusted due to changes in ambient air and in the initial lint moisture content. Proper adjustment of the drying system cannot be made without measuring the moisture content of the dried lint.
At present, annual cotton production in the United States is approximately 14 million bales; with these being processed by 1600 domestic cotton gins. Accurate measurement of moisture content during gin processing will bring about a fuel savings of $0.50 per bale while simultaneously realizing a value improvement of approximately $10 per bale due to the reduction in fiber damage caused by excessive moisture reduction.
In commercial resistance moisture meters all the electrode arrays are connected in series, parallel, or a combination of series and parallel. The resistance measurement of each individual electrode array is relatively high. If these measurements are connected in series, the total resistance of the circuit soon becomes so large that the resistance cannot be measured with currently available techniques. If the number of electrode arrays requisite for a statistically significant sample are used, it is not possible to measure in series their cumulative resistance accurately enough to obtain a reliable moisture reading.
If the resistances are connected in parallel the resulting resistance is a nonlinear representation of all of the measured resistances. This total resistance is smaller than the individual resistances so it can be accurately measured, however, the nonlinear combination of the individual sample resistances disproportionately emphasizes the smaller resistances and biases the representative resistance.
In addition, the relationship between resistance and moisture content is nonlinear. When the resistance is converted to moisture content by means of linearizing equations or linearizing electronics the smaller resistances are given more weight in determining the mean during calibration, skewing the relationship in the same direction as the parallel resistance combination does, thereby exacerbating the problem. In the application of traditional measurements and analysis, the variation in moisture which naturally occurs in the samples is treated in such a way that the results are skewed, resulting in lowered accuracy. Additionally, commercial sensors do not correct for large differences in resistance caused by changes in the temperature of the sensor or the temperature of the solid.
Resistance has been used to measure the moisture content of agricultural materials for many years and a number of related publications have been published. Fairchild et al., U.S. Pat. No. 2,063,840 disclose a moisture testing device for various kinds of material including cotton based on measuring electrical resistance. Multiple electrodes which are electrically in common are used. Means are provided to compress the tested material about the electrode to such a degree that a large and uniform area of contact between the electrodes and the material may be established for successive samples. The use of sample temperature compensation, pressure indication and the determination of resistance/moisture relationships are discussed.
Moore et al., U.S. Pat. No. 3,005,154 discloses moisture testing systems based on electrical resistance and relates to problems presented by ascertainment of a single resistance value based on a plurality of electrical paths through the test material. This is done primarily for the purpose of obtaining an approximation of the average moisture content of plural bodies or samples of material.
Smith, U.S. Pat. No. 3,370,360 discloses an apparatus for analyzing moisture content of materials including cotton having contact electrodes for resistance measurement. A number of parallel electrodes may be utilized so as to contact a large number of random pieces of material. A pulse generator produces electrical pulses at a frequency controlled by the resistance between electrodes. The pulses are produced by the charge and discharge of the capacitor.
Mangialardi et al. (USDA, ARS Prod. Res. Report No. 128; 1971) describe several electrode configurations for continuous measurement of cotton moisture incorporated into roller systems. Employment of large electrode areas was found to cause decreases in resistance greater than what could be attributed to area alone. Their explanation for this behavior was that electrical current seeks the path of least resistance (i.e., the dampest cotton). The greater the electrode area; the greater the chance of including damp cotton in the measurement.
Anthony, U.S. Pat. No. 5,087,120 discloses a system for analyzing entrained solids such as cotton for properties selected from the group consisting of color, trash content, moisture content and combinations thereof. A pressing means in the form of a rotatable plate is taught that presses the mass to be measured against an interior conduit surface to form a face of uniform cotton density that may be analyzed for such properties. Resistance devices are referenced for moisture measurement.
Anthony et al., U.S. Pat. No. 5,125,279 disclose an alternate system to that shown in U.S. Pat. No. 5,087,120 for the same purpose of analyzing entrained solids such as cotton for properties selected from the group consisting of color, trash content, moisture content and combinations thereof. The pressing means taught is in the form of a retractable ram that presses the mass to be measured against an interior conduit surface to form a face of uniform cotton density that may be analyzed for such properties.
Nelson et al., U.S. Pat. No. 5,218,309 disclose means for non-destructively measuring the moisture content of singular agricultural products by use of a parallel plate electrode assembly to measure at least two independent parameters of complex electrical impedance or admittance.
Byler (1992 Proceedings Beltwide Cotton Conference, pp. 1389-1391; and ASAE Paper No. 923032; June 1992) describes equations for the determination of cotton moisture content from resistivity measurements.